L1953s with no 5V

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  • RethoricalCheese
    Badcaps Legend
    • Mar 2013
    • 1517
    • Estonia
    #1

    L1953s with no 5V

    So I got this LG LCD that had the obvious problem - bad caps.

    Changed the caps but for the first time after about a hundred LCD fixes I had soldered one of the caps on the wrong way. That cap just blew up so I changed it for a fresh one, this time correctly.

    Tried it on and... LED light turns on for half a second or so and then just turns off again. Nothing else happens.

    So I took it apart again and saw that there was no 5V present.
    When I disconnected the powerboard from the mainboard, let it wait a little and then connected the powerboard to the AC, there was a nice 5V and 12V was about 16V. Connecting the mainboard made the 5V disappear again and voltage on 12V was dropping about 0.1V per second, doesn't matter if AC was connected or not (so it was just a cap discharging).

    I have tried another mainboard but the problem is still there. I don't have a working powerboard to test the mainboards though.

    Furthermore, I have tried disconnecting the inverter part from the rest of the powerboard by removing J1 jumper. Still the same problem.

    Any ideas what to check?
    Tags: None
    • Porto
      Senior Member
      • May 2015
      • 109
      • NL
      #2
      Re: L1953s with no 5V

      Guess you have a short to ground on that 5v line on the powerboard.
      Maybe in the progress it shorted a mosfet or the driver IC?
      Also check the diodes on that rail.

      Can you post highres pictures of the powerboard's back and front side?

        Comment

        • Porto
          Senior Member
          • May 2015
          • 109
          • NL
          #3
          Re: L1953s with no 5V

          I guess this is the same monitor... here is the service manual of it, with block diagrams and schematics of all boards:

          lg/flatron_l1753s

            Comment

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